Material handling includes the processes and equipment employed in the transportation, storage, protection, distribution, and control of materials and goods used in other commercial or industrial processes. A typical example of a material handling system is a warehouse, commonly referred to as a distribution center, in which goods are stored in bulk and picked out in smaller quantities to fulfill orders for such goods.
The rapid growth of online retailing in the recent years has placed pressure on warehouse operations. Compared with traditional “brick-and-mortar” stores, online retailers usually have a significantly larger variety of goods, lower prices, receive far more orders, and must compete with one another on providing a superior customer experience. These new developments translate to the need for larger warehouses, larger diversity of goods stored, faster order picking speed, higher fulfillment accuracy, and lower operation cost overall.
In traditional warehouses, which employs human labor to retrieve goods and assemble orders, the “order pickers” (i.e., the workers who retrieve goods from storage) must walk a lot. Typically, about 60%-70% of a worker's time is spent on walking among rows of storage racks, which becomes a significant contribution to the inefficiency of such a warehouse in daily operation. Various managerial techniques, such as zoning and computerized path optimization, can mitigate this problem, but only to a limited extent. Most contemporary automation technologies (e.g., conveyors, carrousels, A-frames, AS/RS) can further reduce walking, but they are all generally expensive, solve the problem only partially, and often are limited to specific types of goods.
One existing automated solution employs a number of floor-level, wheeled robots that link to and move shelves of items between a storage area and a packing area. Such a solution can replace the need for human workers to walk to and from the storage area to retrieve items. However, this solution is expensive and is confined to a two-dimensional surface, and, thus, utilizes the three-dimensional space of a warehouse poorly.